[Bug middle-end/30568] New: -ftrapping-math should prevent folding/dead code stripping of some builtins

[Bug middle-end/30568] New: -ftrapping-math should prevent folding/dead code stripping of some builtins

[geoffk at gcc dot gnu dot org]

This program:

#include <stdio.h>
#include <math.h>
#include <fenv.h>

main()
{
unsigned flags;

feclearexcept(FE_ALL_EXCEPT);
(void)acos(1.1);
flags = fetestexcept(FE_ALL_EXCEPT);

printf("(void)acos( %e ) gives flags 0x%8x\n", 1.1, flags & FE_ALL_EXCEPT);
}

when compiled with -ftrapping-math, should show that some flags are set,
FE_INVALID I think (maybe others).  Instead it shows that no flags are set,
because GCC has completely folded out the call to acos().


-- 
           Summary: -ftrapping-math should prevent folding/dead code
                    stripping of some builtins
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: geoffk at gcc dot gnu dot org
GCC target triplet: *-*-darwin*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30568

[Bug middle-end/30568] -ftrapping-math should prevent folding/dead code stripping of some builtins

[geoffk at gcc dot gnu dot org]

------- Comment #1 from geoffk at gcc dot gnu dot org  2007-01-24 02:11 -------
Other builtins where this can apply are pow() and lround().


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30568

[Bug middle-end/30568] -ftrapping-math should prevent folding/dead code stripping of some builtins

[joseph at codesourcery dot com]

------- Comment #2 from joseph at codesourcery dot com  2007-01-24 02:37 -------
Subject: Re:   New: -ftrapping-math should prevent
 folding/dead code stripping of some builtins

On Wed, 24 Jan 2007, geoffk at gcc dot gnu dot org wrote:

> when compiled with -ftrapping-math, should show that some flags are set,
> FE_INVALID I think (maybe others).  Instead it shows that no flags are set,
> because GCC has completely folded out the call to acos().

I think this is the same as bug 29186.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30568

[Bug middle-end/30568] -ftrapping-math should prevent folding/dead code stripping of some builtins

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2007-01-24 06:54 -------
Part of the problem here is that darwin turns on no math-errno by default which
turns the builtin functions into pure functions and since we don't use the 
result, we DCE it.
pure functions are not allowed to trap IIRC the rules.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30568

[Bug middle-end/30568] -ftrapping-math should prevent folding/dead code stripping of some builtins

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2007-01-24 10:25 -------
This is an (easier) variant of PR29186.  Confirmed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |29186
              nThis|                            |
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-01-24 10:25:28
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30568

[Bug middle-end/30568] -ftrapping-math should prevent folding/dead code stripping of some builtins

[kreckel at ginac dot de]

------- Comment #5 from kreckel at ginac dot de  2009-02-15 20:09 -------
(In reply to comment #4)
> This is an (easier) variant of PR29186.  Confirmed.

The difference between this bug and PR29186 is that this one here can be
explained by failing to correctly treat the exception flags at compile-time
(after const folding), whereas PR29186 is all about code movements that make
these flags unreliable during runtime.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30568

[Bug middle-end/30568] -ftrapping-math should prevent folding/dead code stripping of some builtins

[fxcoudert at gcc dot gnu dot org]

------- Comment #6 from fxcoudert at gcc dot gnu dot org  2009-12-29 21:51 -------
Confirming this as generic, non Darwin-specific bug. On i686-linux with current
trunk:

$ cat a.c
#include <stdio.h>
#include <math.h>
#include <fenv.h>

main()
{
unsigned flags;

feclearexcept(FE_ALL_EXCEPT);
(void)acos(1.1);
flags = fetestexcept(FE_ALL_EXCEPT);

printf("(void)acos( %e ) gives flags 0x%8x\n", 1.1, flags & FE_ALL_EXCEPT);
}
$ gcc a.c -ftrapping-math -O0 -fno-math-errno -lm && ./a.out
(void)acos( 1.100000e+00 ) gives flags 0x       0


-- 

fxcoudert at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
 GCC target triplet|*-*-darwin*                 |
   Last reconfirmed|2007-01-24 10:25:28         |2009-12-29 21:51:37
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30568